CN111740391B - Transient high-frequency power protection method and device for annular direct-current ship power distribution network - Google Patents

Transient high-frequency power protection method and device for annular direct-current ship power distribution network Download PDF

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CN111740391B
CN111740391B CN202010684773.1A CN202010684773A CN111740391B CN 111740391 B CN111740391 B CN 111740391B CN 202010684773 A CN202010684773 A CN 202010684773A CN 111740391 B CN111740391 B CN 111740391B
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cable
frequency power
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CN111740391A (en
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黄文焘
陈少宇
邰能灵
宋海涛
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Locating Faults (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

A transient high-frequency power protection method and device for a power distribution network of an annular direct-current ship are characterized in that high-frequency power on two sides of a cable is calculated, protection starting is carried out when high-frequency power amplitude values on two sides of a certain cable are larger than a starting threshold value, and a fault identification and pole selection stage is started; respectively calculating high-frequency power correlation coefficients at two sides of the positive and negative cables and completing identification of fault cables and selection of fault poles; and when the criterion is established, the judged direct current breakers on the two sides of the fault pole cable act on tripping. The invention uses the power high frequency waveform correlation coefficient of each end generated in fault to form the protection criterion, has good performances of high reliability, selectivity, sensitivity and the like, can detect fault occurrence and judge fault cables and fault poles in a very short time, has good transition resistance capability for different fault situations, has low requirement on the synchronism of double-end data, and is not influenced by the operation mode of a ship power distribution network system and limited by network topology.

Description

Transient high-frequency power protection method and device for annular direct-current ship power distribution network
Technical Field
The invention relates to a technology in the field of smart power grids, in particular to a transient high-frequency power protection method and device for a power distribution network of a ring-shaped direct-current ship.
Background
The ship distribution system device is a device used for receiving and distributing ship electric energy, protecting, measuring and adjusting a generator and a power grid, and is formed by combining various electrical equipment such as switches, protective electrical appliances, measuring instruments, adjusting and signal devices and the like according to certain requirements. In order to ensure safe and stable operation of a ship power distribution system, a protection technology with high reliability is particularly important. The existing protection methods for the ship distribution network comprise overcurrent protection, impedance protection, current differential protection and the like.
The current protection means that three-section current protection is widely adopted at present, and the current principle and the time principle are utilized to meet the requirement of selective protection. However, the direct application of three-stage current protection to a marine power distribution system presents a number of problems, including: 1) the ship distribution system has short cable length and low cable impedance, so that the discrimination of short-circuit current of different fault points is very low, the protection cannot distinguish faults inside and outside the region, and the protection selectivity is greatly reduced; 2) when the fault occurs, the motor load of the harbor vessel injects a large short-circuit current into a fault point, so that the misoperation of a non-fault cable due to the detection of a large feed current can be caused, and the protection reliability is reduced; 3) the action current values of two adjacent stages of protection switches are difficult to set and the protection is difficult to match due to the close short-circuit currents of different fault points; 4) the difference of the fault characteristics between the end fault in the area and the near end fault outside the area is very small, the current protection is difficult to accurately identify the fault cable, the selectivity is difficult to meet, and the influence of the transition resistance and the operation mode is easy to influence; therefore, the safe operation of the ship power distribution system is difficult to ensure by the traditional current three-stage protection.
Distance protection means that the length of a ship power distribution system cable is short and impedance is low, so that when faults occur at different positions, the measured impedance difference calculated by distance protection is small, and the protection selectivity is poor. Meanwhile, because the calculated value of the measured impedance is not large, the measured error and the calculated error are not negligible compared with the measured impedance, so that the distance protection is mistaken when the measurement is interfered or the calculation is deviated, and the reliability of the protection is low. And the distance protection is difficult to realize the rapid and accurate impedance measurement in the short data window, and the protection speed is difficult to meet. It follows that the application of conventional distance protection to ship power distribution systems also has significant drawbacks.
The current differential protection means that the current differential protection needs strict data synchronization, the change rate of the fault current of the cable of the ship power distribution system is large, and a small time difference in the case of an external fault can generate large differential current so as to cause the protection to malfunction. Therefore, the traditional current three-section protection, distance protection and current differential protection are difficult to be directly applied to a ring-shaped direct current ship power distribution system, and the selectivity and the reliability are insufficient.
Aiming at the direct current cable of the annular direct current ship power distribution network, in order to solve the difficulties of setting the traditional protection at a threshold value, protecting matching and overcoming the defects of selectivity and quick-action performance, the invention designs a protection method which has the advantages of easy setting of the protection threshold value, no matching and good selectivity and quick-action performance, solves the technical problem of how to quickly and accurately identify the fault section of the direct current ship power distribution network, and provides a solution for the inapplicability of the traditional protection. The protection scheme designed by the invention can realize quick identification and isolation of the fault section of the direct-current ship power distribution network system and accurate identification of the fault type, is not influenced by the operation mode of the ship power system and limited by the structural topology, and improves the safety stability and the operation reliability of the annular direct-current ship power distribution network.
Disclosure of Invention
The invention provides a transient high-frequency power protection method and device for a power distribution network of a ring-shaped direct-current ship, aiming at the defects in the prior art, the method and device utilize the waveform correlation coefficient of power high-frequency quantity at each end generated in fault to form a protection criterion, have good performances such as high reliability, selectivity, sensitivity and the like, and can detect the occurrence of the fault and judge fault cables and fault poles in a very short time. The protection method has good anti-transition resistance capability and anti-noise interference capability, has low requirement on the synchronism of double-end data, and is not influenced by the operation mode of a ship power distribution network system and limited by network topology.
The invention is realized by the following technical scheme:
the invention relates to a transient high-frequency power protection method for a power distribution network of a ring-shaped direct-current ship, which comprises the steps of calculating high-frequency power on two sides of a cable, protecting and starting when the amplitude of the high-frequency power on two sides of a certain cable is larger than a starting threshold value, and entering a fault identification and pole selection stage; respectively calculating high-frequency power correlation coefficients at two sides of the positive and negative cables and completing identification of fault cables and selection of fault poles; and when the criterion is established, the judged direct current breakers on the two sides of the fault pole cable act on tripping.
The invention relates to a high-frequency power protection device of a multi-end annular direct-current ship power distribution network, which comprises: the high-frequency voltage and high-frequency current measuring and taking unit is used for extracting the amplitude and the phase angle of high-frequency voltage at two sides of the cable and the amplitude and the phase angle of high-frequency current in real time; the system comprises a high-frequency power calculation unit, a correlation coefficient calculation unit, a fault starting logic unit and a fault identification and pole selection logic unit, wherein the high-frequency power calculation unit is used for calculating the high-frequency power at two sides of a cable in real time, the correlation coefficient calculation unit is used for calculating the correlation coefficient of the high-frequency power at two sides of the cable in a time window of 2ms after a fault occurs, the fault starting logic unit is used for quickly starting a protection algorithm after the fault occurs, and the fault identification and pole selection logic unit is used for quickly and; the relay unit sends a tripping signal to the corresponding direct current circuit breaker according to a fault judgment result; the direct current Circuit Breaker unit adopts a Solid-state Circuit Breaker (SSCB) for quickly breaking the short-Circuit current of a fault cable and realizing the timely isolation of a fault section; the direct-current arc extinguishing unit is used for rapidly extinguishing arc in the direct-current breaker action moment.
Technical effects
The invention integrally solves the technical problems of the difficult points of setting the threshold value and protecting the matching of the direct current cable of the annular direct current ship power distribution network for responding to the traditional protection, the defects of selectivity and quick action and how to quickly and accurately identify the fault section of the direct current ship power distribution network.
Compared with the prior art, the method takes the correlation coefficient as the basis of fault identification and pole selection, and the correlation coefficient of the fault cable is 1, and the correlation coefficient of the non-fault cable is-1, so that the fault identification discrimination is better, the correlation coefficient threshold values of all the direct current cables can be constant values of 0.5, and complex threshold value setting calculation and comparison and matching of adjacent cable protection threshold values are not required. And when the topological structure of the ship system changes or the operation mode changes, the correlation coefficient threshold value does not need to be changed, and the method can be applied to various network structures such as a ring type network structure, a radiation type network structure, a two/multi-terminal power supply network structure and the like. In addition, in the protection scheme in the prior art, a fault pole selection criterion needs to be newly established and acts after a fault identification criterion, the correlation coefficient criterion provided by the invention not only can realize the identification of a fault cable, but also can realize the fault pole selection at the same time, and no additional pole selection criterion is needed.
Drawings
FIG. 1 is a schematic diagram of a topological structure of a ring-shaped direct current ship power distribution network system;
in the figure: cable 1-Cable 4 are four direct current cables forming a ring topology structure; F1-F4 are different fault positions; 1-8 are protection devices configured for the direct current cable, and the protection devices comprise measuring devices, relays, direct current circuit breakers and other equipment;
FIG. 2 is a schematic diagram of a fault frequency domain additional network for an intra-zone fault;
FIG. 3 is a schematic diagram of a fault frequency domain additional network for an out-of-band fault;
FIG. 4 is a schematic diagram of a fault frequency domain additional network for a non-faulted pole at a single pole fault;
FIG. 5 is a schematic diagram of a protection scheme flow;
fig. 6 is a schematic diagram of a high frequency power protection device.
Detailed Description
As shown in fig. 1, the ± 4kV multi-terminal ring-shaped dc ship distribution network topology implemented by the method includes: the device comprises measuring devices, relays, direct current breakers and other devices, four direct current cables which are connected in series with the devices and form a ring-shaped topological structure, an AC/DC converter station which is respectively connected with direct current buses at each end, ship alternating current systems G1 and G2 which are connected with the AC/DC converter station, a propulsion motor M and an alternating current load L.
The alternating current system, the propulsion motor and the load form a ring-shaped topological structure through the current converter and the direct current cable, the operation mode is flexible, and the ring-opening operation and the ring-closing operation can be realized. Each converter can stabilize the voltage of the direct current bus and maintain power balance through master-slave control or droop control. When any point of F1-F4 on the annular direct current Cable Cable 1-4 breaks down, the direct current circuit breakers on two sides of the broken Cable act rapidly to isolate the fault, the rest parts can work normally, the system operates in an open loop mode, a power loss source and a load loss state do not exist, and power loss is reduced.
The specific implementation parameters in the simulation verification are as follows: the high-frequency electric quantity frequency is 2000Hz, and the data sampling frequency is 10 kHz. The fault occurs at time t-0.4 s. The four direct current cables adopt PI models, and the lengths of the four direct current cables are 4 km. The rated voltage of the direct current system is +/-4 kV; rated line voltages of ship alternating current systems G1 and G2 are 6.6 kV; the rated line voltage of the motor M is 3.8kV, and the rated power is 1.6 MW; the rated power of the ac load L is 1 MW.
As shown in fig. 2, a fault frequency domain additional network for a fault in a zone, m and n represent bus bars on both sides of a protected cable; f is a fault point; u shapefA high frequency voltage source at a fault point; rgIs a transition resistance; zmAnd ZnRespectively representing the high-frequency impedance of the cable at the distance of m and n of the bus from the fault point; zsmAnd ZsnRespectively representing the equivalent high-frequency impedance at the back sides of the bus bars m and n; u shapemAnd UnRespectively representing the high-frequency voltages of the buses m and n; i ismAnd InRespectively representing high-frequency currents flowing to the cable by the bus bars m and n; the arrow direction indicates the reference positive direction of the high-frequency voltage and current.
From fig. 2, the relationship between the high-frequency voltage and the high-frequency current on the m and n sides is:
Figure BDA0002587134650000041
the high-frequency current ratio and the high-frequency voltage ratio of the m side and the n side are respectively as follows:
Figure BDA0002587134650000042
high frequency voltage current phase difference of m and n sides
Figure BDA00025871346500000412
And
Figure BDA0002587134650000043
satisfies the following conditions:
Figure BDA0002587134650000044
the ratio relation of the high-frequency power at the two sides of the cable is as follows:
Figure BDA0002587134650000045
therefore, the ratio of the high-frequency power on the two sides of the cable can be used by a direct proportionality coefficient k1Is represented by, i.e. Pm＝k1×PnWhen the fault occurs in the area, the high-frequency power on the two sides of the cable is in a proportional linear relation.
The out-of-range fault is as follows: taking an n-side out-of-area fault as an example, a fault frequency domain additional network is shown in fig. 3, and an m-side out-of-area fault can be analyzed in the same way. ZmnRepresenting the high frequency impedance of the protected cable; znfRepresenting the equivalent high-frequency impedance from the fault point to the bus n; zsfRepresenting the equivalent high frequency impedance at the backside of the fault point.
From fig. 3, the relationship between the high-frequency voltage and the high-frequency current on the m and n sides is:
Figure BDA0002587134650000046
the high-frequency current ratio and the high-frequency voltage ratio of the m side and the n side are respectively as follows:
Figure BDA0002587134650000047
high frequency voltage current phase difference of m and n sides
Figure BDA0002587134650000048
And
Figure BDA0002587134650000049
satisfies the following conditions:
Figure BDA00025871346500000410
the ratio relation of the high-frequency power at the two sides of the cable is as follows:
Figure BDA00025871346500000411
therefore, the ratio of the high-frequency power on the two sides of the cable can use a negative proportionality coefficient k2Is represented by, i.e. Pm＝k2×PnWhen the area is out of range fault, the high frequency power at two sides of the cable is in linear relation of negative proportion.
When the single pole is in fault, the positive and negative DC cables are coupled, so that the non-fault pole cableA high frequency electrical quantity is induced. In the fault frequency domain additional network, only the fault pole cable contains a fault high-frequency voltage source, and the non-fault pole cable does not contain a fault high-frequency voltage source, and for the non-fault pole with a single pole fault, the fault frequency domain additional network is shown in fig. 4. U in the figurem、Un、Im、InAre high frequency electrical quantities generated by faulty pole coupling. I ismAnd InOpposite phase, UmAnd UnThe phase of the signals is approximately the same,
Figure BDA0002587134650000059
and
Figure BDA00025871346500000510
the difference is about 180 degrees, so the high-frequency power on both sides of the non-fault pole cable is in a linear relationship with a negative proportion.
The different fault types include: the linear relationship of high-frequency power on two sides of the cable with different fault types is shown in table 1.
TABLE 1 Cable two-side high-frequency Power Linear relationship for different failure types
Figure BDA0002587134650000051
Calculating high-frequency voltage, current amplitude and phase angle at two sides of the cable in real time by using a sliding data window function of a Fourier transform algorithm, and calculating high-frequency power
Figure BDA0002587134650000052
Wherein: k is the sampling point serial number; i Um(k) I and Im(k) L represents the amplitude of the high-frequency voltage and current on the m side respectively;
Figure BDA0002587134650000055
and
Figure BDA0002587134650000056
respectively represent m-side high-frequency voltages andthe phase angle of the current; i Un(k) I and In(k) L represents the amplitude of the high-frequency voltage and current of the n side respectively;
Figure BDA0002587134650000057
and
Figure BDA0002587134650000058
respectively representing the phase angles of the high-frequency voltage and the current of the n side; pm(k) And Pn(k) Respectively representing the high frequency power at the sampling point time on the m and n sides.
High-frequency power correlation coefficients of two sides of the positive and negative cables
Figure BDA0002587134650000053
Wherein: s is the total number of sampling points in a 2ms time window; k is the serial number of the sampling point in the time window (k is 1,2,3, …, s), counting is started after the fault is started, and the correlation coefficient is calculated after the time window is full to serve as output; rhomnRepresenting the correlation coefficient of the high frequency power on both sides of the cable.
The correlation coefficient is characterized by Pm(k) And Pn(k) When the same sign is satisfied, rho is more than 0mnLess than or equal to 1, and the correlation coefficient is a positive value; when they are of opposite sign, -1. ltoreq. rhomnIf the correlation coefficient is less than 0, the correlation coefficient is a negative value; when they satisfy the direct proportional linear relationship, there is ρmn1 holds true; when they satisfy the negative proportional linear relationship, there is ρmnThe true is true for-1. The linear relationship in table 2 can be described more accurately and observably by the correlation coefficient. Table 2 shows the correlation coefficient results corresponding to table 1.
TABLE 2 high-frequency power correlation coefficient of two sides of cable for different fault types
Figure BDA0002587134650000054
Figure BDA0002587134650000061
The criteria comprise fault starting criteria, fault identification and pole selection criteria.
The fault starting criterion is as follows: under the condition of meeting a certain frequency selection, the high-frequency power at the protective installation position is almost 0 during normal operation; only after the fault occurs, the protection site will detect high frequency power with a large amplitude. The fault starting criterion is formed by using the characteristic:
Figure BDA0002587134650000062
wherein: i Pm(k) I and I Pn(k) I represents the amplitude of the high-frequency power at the m and n sides of the cable; i PsetAnd | is a set starting threshold, is set according to the maximum amplitude of the high-frequency power detected at the protection installation position when the normal operation is avoided, and is taken as 0.01kW in consideration of a certain margin.
And when the amplitudes of the high-frequency power at the two sides of the cable are both larger than a set threshold value, starting protection, and entering a fault identification and pole selection stage.
The fault identification and pole selection criterion is as follows: respectively calculating the correlation coefficients of the high-frequency power at two sides of the anode cable
Figure BDA0002587134650000065
Coefficient of correlation with high-frequency power on two sides of negative cable
Figure BDA0002587134650000063
According to table 1, the fault identification and pole selection criteria are:
Figure BDA0002587134650000064
wherein: rhosetFor a set correlation coefficient threshold, a positive number, which may be 0.5, is set to distinguish between different fault types.
When the fault occurs in the area, the correlation coefficient of the fault pole cable is close to 1 and is far greater than the threshold value of 0.5; for non-faulted pole cables and out-of-range fault conditions, the correlation coefficient is close to-1, much less than the threshold 0.5. The criterion therefore has a good degree of discrimination between the types of faults.
As shown in fig. 5, in the transient high-frequency power protection method for the power distribution network of the ring-shaped direct-current ship according to this embodiment, high-frequency powers on two sides of a cable are calculated, and when the high-frequency power amplitudes on two sides of a certain cable are both greater than a start threshold, start-up protection is performed, and a fault identification and pole selection stage is performed; respectively calculating high-frequency power correlation coefficients at two sides of the positive and negative cables and completing identification of fault cables and selection of fault poles; and when the criterion is established, the judged direct current breakers on the two sides of the fault pole cable act on tripping.
As shown in fig. 6, the high-frequency power protection device for a multi-terminal ring-shaped dc ship distribution network according to this embodiment includes:
the system comprises a voltage transformer unit for measuring the direct current bus voltage at two ends of a cable in real time, a current transformer unit for measuring the current flowing to the cable from the direct current bus in real time, and a high-frequency voltage and high-frequency current measuring unit which is respectively connected with the voltage transformer unit and the current transformer unit, wherein the high-frequency voltage and high-frequency current measuring unit is designed according to a discrete Fourier algorithm and is used for extracting the high-frequency voltage amplitude and phase angle and the high-frequency current amplitude and phase angle at two sides of the cable in real time;
the system comprises a high-frequency power calculation unit, a correlation coefficient calculation unit, a fault starting logic unit and a fault identification and pole selection logic unit, wherein the high-frequency power calculation unit is used for calculating the high-frequency power at two sides of a cable in real time, the correlation coefficient calculation unit is used for calculating the correlation coefficient of the high-frequency power at two sides of the cable in a time window of 2ms after a fault occurs, the fault starting logic unit is used for quickly starting a protection algorithm after the fault occurs, and the fault identification and pole selection logic unit is used for quickly and;
the relay unit sends a tripping signal to the corresponding direct current circuit breaker according to a fault judgment result; the direct current Circuit Breaker unit adopts a Solid-state Circuit Breaker (SSCB) for quickly breaking the short-Circuit current of a fault cable and realizing the timely isolation of a fault section; the direct-current arc extinguishing unit is used for rapidly extinguishing arc in the direct-current breaker action moment.
The high-frequency electric quantity frequency is 2000Hz, and the data sampling frequency is 10 kHz. The fault occurs at time t-0.4 s. The start threshold was taken to be 0.01kW to detect the occurrence of a fault and the correlation coefficient threshold was taken to be 0.5 to distinguish the type of fault. The following simulation experiments were made.
In the present embodiment, table 3 and table 4 show simulation results when Cable1 is used as an analysis object to obtain the internal and external faults of different fault types. In the table
Figure BDA0002587134650000071
The correlation coefficient represents the high-frequency power on two sides of the positive cable of the cable i;
Figure BDA0002587134650000072
and the correlation coefficient of the high-frequency power on the two sides of the negative cable of the cable i is shown.
TABLE 3 Fault discrimination results for various in-zone faults
Figure BDA0002587134650000073
TABLE 4 Fault discrimination results for various out-of-zone faults
Figure BDA0002587134650000074
Figure BDA0002587134650000081
From tables 3 and 4, when a single-pole fault occurs in a zone, the correlation coefficient of only a Cable1 fault pole Cable is close to 1, and the correlation coefficients of a Cable1 non-fault pole Cable and the correlation coefficients of the rest cables (Cable 2-Cable 4) are close to-1; when the bipolar fault occurs in the region, the correlation coefficients of the Cable1 positive and negative cables are close to 1, and the correlation coefficients of the other non-fault cables (Cable 2-Cable 4) are close to-1; when an outside fault occurs, the correlation coefficients of the Cable1 positive and negative cables are close to-1, the protection of the Cable1 judges that the outside fault strictly does not act, and other cables can correctly judge the fault Cable and the fault pole according to the correlation coefficients, for example, when the F2 positive pole fails, only the high-frequency power correlation coefficients at two sides of the Cable2 positive pole Cable
Figure BDA0002587134650000083
And the correlation coefficients corresponding to the other cables are close to-1, and the protection criterion is judged to be the positive fault of Cable 2. By combining the table 3 and the table 4, for cable faults of different fault positions and fault types, the correlation coefficient of a fault cable is far greater than the threshold value of 0.5, the correlation coefficient of a non-fault cable is far less than the threshold value of 0.5, the protection scheme can accurately judge the fault cable and the fault pole, and the transition resistance tolerance capability is good.
This example further analyzes the effect of transition resistance on protection performance: the fault frequency domain additional network shown in fig. 2 and fig. 3 considers the transition resistance, but the transition resistance does not change the relational expression between the high-frequency voltage and the high-frequency current, the positive-negative proportional linear relation of the high-frequency power at two sides of the cable is not influenced, the linear relation can be accurately described by the related coefficient, and the protection method has good anti-transition resistance capability. As can be seen from tables 3 and 4, the transition resistance has almost no influence on the correlation coefficient of each cable, and the fault section and the fault pole can be accurately determined according to the correlation coefficient of each cable, so that the transition resistance capability is good.
This example further analyzes the impact of data dyssynchrony on protection performance: the data asynchronization only leads the change moment of the high-frequency power at one side of the cable to lag behind the change moment at the other side, but the change trend and the positive and negative properties of the high-frequency power are unchanged, namely, the data asynchronization does not influence the linear relation between the positive and negative directions and the positive and negative proportion of the high-frequency power change at the two sides of the cable, so the influence of the data asynchronization on the protection performance can be. Data on two sides of Cable1 are not synchronous, time difference is 1-1000 mus, and correlation coefficient and fault judgment result of each Cable are shown in table 5. Although the larger time difference can slightly reduce the correlation coefficient result of the fault cable, the time difference is still far higher than the threshold value of 0.5, and the protection can still accurately select the fault cable.
TABLE 5 Fault discrimination results for data asynchronism
Figure BDA0002587134650000082
Figure BDA0002587134650000091
Analyzing the influence of the operation mode and the topological structure of the ship system on the protection performance: for the annular direct current ship system in fig. 1, there are more flexible operation modes and corresponding multiple topology structures, and when the system is operated in an open loop (for example, circuit breakers at 5 and 6 of Cable3 are disconnected), the system is equivalent to a two/multiple-terminal power supply structure; when the loop closing operation is carried out (all the circuit breakers at the positions 1-8 are closed), the loop closing operation is equivalent to a looped network structure. Tables 3 and 4 are simulation results of the looped network, so it is necessary to analyze whether the protection is effective or not when the cable fails in the looped network operation mode, and verify the applicability of different topology structures for protecting the looped network and two/more terminals for power supply. The system operation mode is open loop (circuit breakers at 5 and 6 are opened, Line3 is exited), and when different types of faults occur in Line1, Line2 and Line4, the correlation coefficient and the fault discrimination result are shown in table 6. By combining the open-loop table 6 and the closed-loop simulation result tables 3 and 4, the fault cable and the fault pole can be accurately judged no matter what operation mode the looped network is, and the protection scheme is not influenced by the operation mode of the system. In addition, the closed-loop operation is equivalent to a ring network structure, and the open-loop operation is equivalent to a two/multi-terminal power supply structure, so the protection scheme is suitable for various network topological structures.
TABLE 6 Fault discrimination results in open-Loop operation mode
Figure BDA0002587134650000092
Analyzing the influence of noise interference on the protection performance: the protection method of the invention is to utilize high-frequency active power to identify fault cables, and the source of the fault cables is the amplitude and phase angle of high-frequency voltage and high-frequency current. High frequency voltages and currents are susceptible to noise interference, and it is therefore necessary to analyse the effect of signal noise on fault identification criteria. The noise interference can increase or reduce the amplitude of the high-frequency active power to a certain degree, but as long as the sampling points in the data window are enough, the positive and negative change trends of the high-frequency active power on the two sides of the cable can be still accurately reflected. The correlation coefficient protection method has higher protection reliability because a plurality of sampling point data in a 2ms data window are utilized. Therefore, the protection method has good anti-noise interference capability. The signal noises with different intensities can be replaced by Gaussian noises with different signal-to-noise ratios, the signal noises with different intensities are added into the voltage and current sampling sequences of each protection device, and the correlation coefficient result and the fault cable identification result are shown in table 7. The smaller the signal-to-noise ratio, the greater the noise intensity, and the good characteristics of the correlation coefficient of each cable are maintained even under the condition of large noise interference with the signal-to-noise ratio of 20 dB. The signal noise with different intensity has almost no influence on the correlation coefficient result of each cable, and the fault cable can be accurately identified. The protection method is thus very robust against noise interference effects.
TABLE 7 determination of faults in different signal noises
Figure BDA0002587134650000101
To sum up, compared with the prior art, the technical effects of the embodiment include: 1) by utilizing the unique fault characteristics of the high-frequency electric quantity, the complex steady-state load flow calculation and fault electric quantity calculation required by conventional protection are effectively avoided, and the problems of difficult setting of threshold, insufficient selectivity and the like when the conventional protection is applied to the annular direct-current ship power distribution network are solved; 2) the fault identification and pole selection criterion is formed by using the correlation coefficient, so that the accurate identification of the fault position and type can be realized, the threshold value of each cable is easy to set, and the comparison and the matching of the adjacent cable protection threshold values are not needed; 3) the correlation coefficient principle can be simultaneously applied to fault cable identification and fault pole selection, extra pole selection criteria are not needed, the fault cable and the fault pole can be rapidly and reliably judged within 3ms by the protection scheme, and the protection speed and the protection selectivity are good; 4) the protection scheme has strong transition resistance tolerance capability, low requirement on data synchronization, good fault identification discrimination, good protection reliability and good sensitivity; 5) the protection method is not only suitable for an annular direct current ship power distribution network, but also suitable for various topological structures such as two-end power supply, radiation type, mesh type and the like; 6) the set threshold value of the protection does not need to be changed according to the change of the network structure or the operation mode of the ship system, and the protection method can be applied to various topological structures, is not influenced by the operation mode and has good popularization prospect.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (6)

1. A transient high-frequency power protection method for a power distribution network of an annular direct-current ship is characterized in that high-frequency power on two sides of a cable is calculated, when the amplitude of the high-frequency power on two sides of a certain cable is larger than a starting threshold value, protection starting is carried out, and a fault identification and pole selection stage is started; respectively calculating high-frequency power correlation coefficients at two sides of the positive and negative cables and completing identification of fault cables and selection of fault poles; when the criterion is established, the judged direct current circuit breakers on the two sides of the fault pole cable act on tripping;
high-frequency power correlation coefficients of two sides of the positive and negative cables
Figure FDA0002931230020000011
Wherein: s is the total number of sampling points in a 2ms time window; k is the serial number of the sampling point in the time window (k is 1,2,3, …, s), counting is started after the fault is started, and the correlation coefficient is calculated after the time window is full to serve as output; rhomnA correlation coefficient representing high-frequency power on two sides of the cable; when P is presentm(k) And Pn(k) When the same sign is satisfied, rho is more than 0mnLess than or equal to 1, and the correlation coefficient is a positive value; when they are of opposite sign, -1. ltoreq. rhomnIf the correlation coefficient is less than 0, the correlation coefficient is a negative value; when they satisfy the direct proportional linear relationship, there is ρmn1 holds true; when they satisfy the negative proportional linear relationship, there is ρmnThe true is true for-1.
2. The method for transient high-frequency power protection of a power distribution network of a ring-shaped direct current ship as claimed in claim 1, wherein the identification of the fault cable and the selection of the fault pole comprise: an out-of-zone fault, an in-zone negative ground fault, an in-zone bipolar short fault, and an in-zone positive ground fault.
3. The method for protecting transient high-frequency power of the power distribution network of the annular direct current ship as claimed in claim 1, wherein the criteria comprise fault starting criteria, fault identification and pole selection criteria.
4. The ring-shaped direct current ship power distribution network transient high-frequency power protection method according to claim 3, wherein the fault starting criterion is as follows: the high-frequency power at the protection installation position is almost 0 in normal operation; and after the fault happens, judging the fault starting:
Figure FDA0002931230020000012
wherein: i Pm(k) I and I Pn(k) I represents the amplitude of the high-frequency power at the m and n sides of the cable; i PsetAnd | is a set starting threshold, when the amplitudes of the high-frequency power at the two sides of the cable are both larger than the set threshold, the protection is started, and a fault identification and pole selection stage is carried out.
5. The ring-shaped direct current ship power distribution network transient high-frequency power protection method as claimed in claim 3, wherein the fault identification and pole selection criterion is as follows: respectively calculating the correlation coefficients of the high-frequency power at two sides of the anode cable
Figure FDA0002931230020000013
Coefficient of correlation with high-frequency power on two sides of negative cable
Figure FDA0002931230020000021
The fault identification and pole selection criterion is as follows:
Figure FDA0002931230020000022
wherein: rhosetIs a set correlation coefficient threshold.
6. An annular direct current ship power distribution network transient high-frequency power protection system for realizing the method of any one of claims 1-5, which is characterized by comprising the following steps:
the high-frequency voltage and high-frequency current measuring and taking unit is used for extracting the amplitude and the phase angle of high-frequency voltage at two sides of the cable and the amplitude and the phase angle of high-frequency current in real time;
the system comprises a high-frequency power calculation unit, a correlation coefficient calculation unit, a fault starting logic unit and a fault identification and pole selection logic unit, wherein the high-frequency power calculation unit is used for calculating the high-frequency power at two sides of a cable in real time, the correlation coefficient calculation unit is used for calculating the correlation coefficient of the high-frequency power at two sides of the cable in a time window of 2ms after a fault occurs, the fault starting logic unit is used for quickly starting a protection algorithm after the fault occurs, and the fault identification and pole selection logic unit is used for quickly and;
the relay unit sends a tripping signal to the corresponding direct current circuit breaker according to a fault judgment result; the direct current breaker unit adopts a solid-state switch and is used for quickly breaking the short-circuit current of a fault cable and realizing the timely isolation of a fault section; the direct-current arc extinguishing unit is used for rapidly extinguishing arc in the direct-current breaker action moment.
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